The mean of the area and a size-class distribution of the glomeruli were calculated with a computer-assisted planimeter in a series of autopsy specimens from subjects without any evidence of renal disease. These morphometric variable were also related to the severity of histologic glomerular lesions, graded on a four class scale. Glomerular size was independent of body mass index and kidney weight. This morphometric analysis was compared with that obtained from a series of forensic autopsies from Caucasians matched for age and sex. The mean glomerular volume was greater in the Pima Indians than in the Caucasians. Furthermore the volume fraction of the cortex occupied by the glomeruli was greater in the Pima Indians, suggesting that their increased glomerular volume was not due to a reduced number of glomeruli. The large size of the glomeruli in the Pima Indians was independent of obesity or heart weight and could constitute a genetic trait of this population. In this population the changes in glomerular mass and filtration surface may underlie a familial predisposition to developing renal disease. Finally we undertook a similar study in a series of forensic autopsies in African Americans since their incidence of end stage renal disease is much higher than in the caucasian population. The mean size of the glomeruli was significantly greater in the African American population. We postulate that the increased glomerular size may constitute a marker for a sclerosis-prone population.